The Angola Low: relationship with southern African rainfall and ENSO

Crétat, Julien; Pohl, Benjamin; Dieppois, Bastien; Berthou, Ségolène; Pergaud, Julien

doi:10.1007/s00382-018-4222-3

Cited by 52 publications

(55 citation statements)

References 39 publications

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“…The Angola low forms over a plateau region in the southern Angola-northern Namibia area in austral summer, at the southern limit of a trough of low pressure extending from Ethiopia, through central Africa, associated with the intertropical convergence zone (Reason et al 2006;Munday and Washington 2017). Variations in the strength of the AL have been associated with both daily (Crétat et al 2018) and interannual precipitation variability (Cook et al 2004;Munday and Washington 2017) over southern Africa. Howard and Washington (2018) found that on a synoptic scale the AL can be separated into the Angola heat low and Angola tropical low, with the precipitation variability more strongly related to the interannual variability of the tropical lows.…”

Section: A Background On Shl and Almentioning

confidence: 99%

“…Given the important role that the SHL and AL play in driving rainfall seasonality and variability over West Africa and the wider Sahel (Lavaysse et al 2009) and southern Africa (Munday and Washington 2017;Crétat et al 2018;Howard and Washington 2018), their influence in a changing climate was investigated. A metric based on the methodology of Biasutti et al (2009) andDixon et al (2017) was used to quantify changes in the strength of the SHL and AL (see section 2).…”

Section: B Future Changes In Shl and Almentioning

confidence: 99%

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Later Wet Seasons with More Intense Rainfall over Africa under Future Climate Change

2018

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Later wet seasons with more intense rainfall over Africa under future climate change Article Published Version Dunning, C., Black, E. and Allan, R. (2018) Later wet seasons with more intense rainfall over Africa under future climate change. Journal of Climate, 31. pp. 97199738. ISSN 0894 8755ABSTRACT Changes in the seasonality of precipitation over Africa have high potential for detrimental socioeconomic impacts due to high societal dependence upon seasonal rainfall. Here, for the first time we conduct a continental-scale analysis of changes in wet season characteristics under the RCP4.5 and RCP8.5 climate projection scenarios across an ensemble of CMIP5 models using an objective methodology to determine the onset and cessation of the wet season. A delay in the wet season over West Africa and the Sahel of over 5-10 days on average, and later onset of the wet season over southern Africa, is identified and associated with increasing strength of the Saharan heat low in late boreal summer and a northward shift in the position of the tropical rain belt over August-December. Over the Horn of Africa rainfall during the ''short rains'' season is projected to increase by over 100 mm on average by the end of the twenty-first century under the RCP8.5 scenario. Average rainfall per rainy day is projected to increase, while the number of rainy days in the wet season declines in regions of stable or declining rainfall (western and southern Africa) and remains constant in central Africa, where rainfall is projected to increase. Adaptation strategies should account for shorter wet seasons, increasing rainfall intensity, and decreasing rainfall frequency, which will have implications for crop yields and surface water supplies.

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Section: A Background On Shl and Almentioning

confidence: 99%

Section: B Future Changes In Shl and Almentioning

confidence: 99%

Later Wet Seasons with More Intense Rainfall over Africa under Future Climate Change

2018

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“…For example, it is widely believed that an anomalously strong Angola Low, coupled with high SSTs in the western Indian Ocean and eastern subtropical South Atlantic Ocean, were partly responsible for reducing the impact of El Nino during the intense 1997/1998 ENSO event, resulting in near-normal seasonal rainfall (Reason and Jagadheesha, 2005;Lyon and Mason, 2009;Hoell et al, 2017;Blamey et al, 2018). Crétat et al (2018) additionally found that the Indian Ocean modes of variability provided favourable background conditions for the development of the anomalous Angola Low. On examination of the strong 2015/2016 El Nino, Blamey et al (2018) report that a much stronger Botswana High was present at the start of the austral summer than in other El Nino events.…”

Section: Example 1: Enso and Droughtmentioning

confidence: 99%

Climate process chains: Examples from southern Africa

Daron

Burgin

Janes

et al. 2019

Intl Journal of Climatology

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The climate system comprises multiple components, primarily the atmosphere, ocean and cryosphere, each incorporating physical processes that interact across scales. To help understand the behaviour of this complex system, and evaluate climate model simulations, researchers typically take a reductionist approach, focusing on individual climate processes and studying their relationships with weather and climate in different regions. While more holistic approaches, such as climate networks, have been developed to explicitly address the complexity of the climate, here we argue for the use of a new approach that accounts for multiple cross‐scale process interactions, framed with respect to specific climate outcomes of societal importance. We introduce and explore the concept of “climate process chains” (CPCs), describing their potential application using examples determined for southern Africa. Building on related theoretical concepts, and through reviewing literature on climate processes and teleconnections to southern Africa, we identify candidate CPCs for two outcomes of societal interest; a regional‐scale drought and local‐scale heavy rainfall. Focusing on such outcomes means that CPC investigations have more relevance to climate risk management contexts, as well as providing a constraint on the exploration of climate uncertainties for a region. We argue that CPCs may help to articulate relationships amongst regionally relevant climate processes across temporal and spatial scales, and discuss their potential utility in climate research, including in the evaluation of climate models and their simulations.

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“…However, this relationship has not been studied on a synoptic time scale. Crétat et al (2018) call for a better understanding of the relationship between the Angola Low and tropical-extratropical interactions on a daily time scale.…”

Section: Introductionmentioning

confidence: 99%

Tropical Lows in Southern Africa: Tracks, Rainfall Contributions, and the Role of ENSO

2019

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Southern African tropical lows are synoptic‐scale cyclonic vortices that propagate westward across southern Africa in the Austral summer. They strongly influence local rainfall and aggregate in the climatological December, January, and February mean to form the Angola Low. In this study, tropical lows are identified and tracked using an objective feature tracking method. The statistics of tropical low tracks over southern Africa are presented and compared across three reanalysis products. Findings are compared to the literature of tropical low‐pressure areas elsewhere in the world, where it is found that most tracking statistics compare well but that the tendency of tropical lows to become semistationary over Angola is unique to southern Africa. The hypothesis that tropical lows in Angola have a causal relationship with Tropical Temperate Troughs is tested, and a correlation between occurrence frequencies is found at interannual but not daily time scales. Precipitation is attributed to the tropical lows, and it is found that tropical lows are associated with 31% of rainfall across tropical southern Africa, based on gridded precipitation products. The interannual variability of the number of tropical lows that form per year (σ=6 events/year) is linked to El Niño–Southern Oscillation (ENSO) and the tropical easterly jet. The mean latitude of tropical lows is shifted northward during El Niño and southward during La Niña. Much of the interannual precipitation variability maximum in Angola is attributed to rainfall associated with tropical lows. These results provide insights into the southern African response to ENSO and into the mechanisms of rainfall in the southern African tropical edge.

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The Angola Low: relationship with southern African rainfall and ENSO

Cited by 52 publications

References 39 publications

Later Wet Seasons with More Intense Rainfall over Africa under Future Climate Change

Later Wet Seasons with More Intense Rainfall over Africa under Future Climate Change

Climate process chains: Examples from southern Africa

Tropical Lows in Southern Africa: Tracks, Rainfall Contributions, and the Role of ENSO

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